1. Field of the Invention
The present invention relates to a method of manufacturing an ink-jet printhead, and more particularly, to a method of improving a shape of a nozzle and effectively anti-wetting a surface of a nozzle plate while manufacturing an ink-jet printhead.
2. Description of the Related Art
Ink-jet printheads may eject ink by using an electro-thermal transducer which generates bubbles in the ink with a heat source, or by using an electromechanical transducer, which causes a volume variation of the ink by deformation of a piezoelectric device.
An ink ejection mechanism includes a top-shooting ink ejection mechanism, a side-shooting ink ejection mechanism, and a back-shooting ink ejection mechanism depending on a growth direction of bubbles and an ejection direction of ink droplets. The top-shooting ink ejection mechanism has a structure in which the growth direction of bubbles is identical with the ejection direction of ink droplets. The side-shooting ink ejection mechanism has a structure in which the growth direction of bubbles is perpendicular to the ejection direction of ink droplets. The back-shooting ink ejection mechanism has a structure in which the growth direction of bubbles is opposite to the ejection direction of ink droplets.
Ink-jet printheads having the above-described structures include a nozzle plate having a nozzle (orifice) through which ink droplets are ejected. The nozzle plate is directly opposite to paper and has several factors which may affect the ejection of ink droplets through the nozzle. The most important factor is a thickness and shape of the nozzle. One of the factors is a hydrophobic property of a surface of the nozzle plate. When the thickness of the nozzle is small or a section thereof has a radial shape, and the hydrophobic property of the surface of the nozzle plate is small (that is, when the nozzle plate is hydrophilic), some of the ink ejected though the nozzle soaks into the surface of the nozzle plate such that the surface of the nozzle plate is contaminated, and a size, direction, and speed of the ejected ink droplets are not constant. In order to solve these problems, the thickness of the nozzle is increased to at least over 10 μm, and a section thereof has a tapered shape. Also, a coating layer to perform anti-wetting is formed on the surface of the nozzle plate.
FIG. 1 is a schematic cross-sectional view of an ink-jet printhead 10 having the back-shooting ink ejection mechanism in which a nozzle plate is anti-wetted. Referring to FIG. 1, a hemispherical ink chamber 14 is formed in a center of a top surface of a substrate 11, a rectangular channel-type manifold 17 is formed under the hemispherical ink chamber 14, and the ink chamber 14 and the manifold 17 are communicated with each other via an ink passage 16. A multi-layer nozzle plate 12 is formed on the top surface of the substrate 11. The nozzle plate 12 is a membrane formed by several different layers stacked on the substrate 11, and includes a nozzle (or orifice) 18 formed in a center of the ink chamber 14, and a bubble guide 18a to extend into the ink chamber 14 around the nozzle 18. The nozzle plate 12 includes a lower insulating layer 12a, an intermediate insulating layer 12b, and an upper insulating layer 12c. A heater 13 which surrounds the nozzle 18 is formed between the lower insulating layer 12a and the intermediate insulating layer 12b, and an interconnection layer 15 to be connected to the heater 13 is formed between the intermediate insulating layer 12b and the upper insulating layer 12c. A pad 22 is also connected between the intermediate insulating layer 126 and the upper insulating layer 12c. 
In the above-described structure, the upper insulating layer 12c is formed by a stack of two or more layers, and a hydrophobic coating layer 19 is formed on the upper insulating layer 12c. The hydrophobic coating layer 19 should be formed at least on a surface around the nozzle 18. Here, the hydrophobic coating layer 19 is formed of metal such as nickel (Ni), gold (Au), palladium (Pd) or tantalum (Ta), perfluoronated alkane and silane compounds with a high hydrophobic property such as fluoronated carbon (FC), F-Silane, or diamond-like carbon (DLC). The hydrophobic coating layer 19 may be formed using a wet deposition method such as spray coating or spin coating, or may be formed using a dry deposition method such as PECVD or sputtering. The hydrophobic coating layer 19 is formed in a state in which the nozzle 18, the bubble guide 18a, the ink chamber 14, the manifold 17, and the ink passage 16 have been already formed. While the hydrophobic coating layer 19 is formed, a hydrophobic material permeates into the ink chamber 14 through the nozzle 18 such that a hydrophobic material layer 19′ is formed on an entire or partial surface of the ink chamber 14, and may also be, in a worse case scenario, formed on an inner wall of the ink passage 16 connected to the manifold 17. Since the hydrophobic material typically rejects ink, the ink may not be smoothly supplied to the ink chamber 14, and the ink chamber 14 may not be totally filled. Moreover, if the hydrophobic material layer 19′ is formed inside the bubble guide 18a, this poorly affects movement of a meniscus 14a of the ink such that good quality ink droplets are not ejected at high speed. Thus, the hydrophobic material is formed on the surface of the nozzle plate 12, and the hydrophobic material layer 19′, which is formed in the ink chamber 14 and the ink passage 16, is removed by a subsequent etch process (i.e., an 02 plasma etch process). However, when the hydrophobic material in the ink chamber 14 is removed by the O2 plasma etch process, the nozzle plate 12, and in particular, the hydrophobic coating layer 19 formed on the surface of the nozzle plate 12, may be overexposed to O2 plasma and thus, damaged greatly.
Since the above-mentioned conventional ink-jet printhead has a back-shooting ink ejection mechanism in which the heater 13 is provided to the nozzle plate 12 having a small thickness, and the growth direction of bubbles is opposite to the ejection direction of ink droplets, the bubble guide 18a formed of tetraethoxysilane (TEOS) should be provided to a nozzle so that an expansion pressure is effectively transferred to ink droplets. In the absence of the bubble guide 18a, a pressure generated by bubbles cannot be sufficiently transferred to the nozzle and thus, ink droplets cannot be stably and rapidly ejected. If the nozzle plate 12 does not have a sufficient thickness, it is essential to form the bubble guide 18a on the nozzle. Preferably, the bubble guide 18a has a height of 30 microns. However, due to limitations of reactive ion etch (RIE) and TEOS processes on Si, it is substantially difficult to form the bubble guide 18a with a height of more than 10 microns.